Durable Coreplate For Improved Electrical Resistance In Electric Equipment And A Process Thereof

ABSTRACT

An improved inter-laminar coating for steel laminations used in electrical equipment such as electric motors, generators and transformers. The invention further includes a process for creating, restoring, and improving the condition of insulation of such equipment using an aqueous solution of phosphoric acid with additives including zinc and/or manganese.

CROSS REFERENCE TO RELATED APPLICATIONS

This claims priority to Provisional patent application 60/726,138 filedOct. 13, 2005 which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None

BACKGROUND OF THE INVENTION

This invention relates to electrical equipment such as electric motors,generators and transformers, and more particularly, to a durablecoreplate for improved electrical resistance in such equipment and aprocess for applying the coreplate.

As is well-known in the electric motor art, steel laminations are usedto form the stator core of an electric motor or generator. Thelaminations are also used to make electrical transformers. Thelaminations, which are electrically insulated from each other, areformed into a stack. The present invention relates to an improvementover previously used interlaminar insulation (aka, coreplate) such asthat described in U.S. Pat. Nos. 3,908,066 and 3,839,256. These patentsdescribe compositions, methods for coating, and coated electrical ormagnetic grade steel for use in the magnetic cores of transformers,motors and generators. The coatings so described have been widely usedin the industry.

There are, however, numerous problems with present coreplate processes.For example, use of sodium silicate is hampered by the fact it iswater-soluble so the coating formed is not durable. Further, the processemployed to form the Fe₃O₄ widely used as an interlaminar insulation inelectrical equipment to develop coreplate, requires careful control oftemperature, oxygen and humidity, as well as extended exposure attemperatures above 400° F. (204° C.). Because of this, the energyrequired to develop Fe₃O₄ often accounts for one-third of the laminationcost.

During operation of a motor or generator, the laminated core vibrates attwice the line frequency. Over time, this results in interlaminarinsulation abrading and deteriorating, resulting in increased operatingtemperatures on portions of the laminations (localized hotspots) thatreduce performance of the equipment, and sometimes cause windingfailure. This is especially problematic in large generators (severalmegawatts and larger) used to produce power. The cost to repair the coredamage, using traditional repair methods, is often beyond economicfeasibility. While a small amount of coreplate deterioration does notsignificantly affect the performance of electric motors, generators ortransformers, it does increase core losses and thereby reducesefficiency of the machine. And, the effect of such damage is cumulative;so, over time, the operating costs of a motor or generator may increase.Evidence of this degradation can be found in reports leading up to theEnergy Policy Act of 1992, and numerous studies before and since.

When coreplate deteriorates, the operating temperature of the motor,generator, or transformer increases, reducing the insulation life of thewindings. When used as a part of the original manufacturing process forthis equipment, the improved coreplate and process of the inventionextends the life of the lamination insulation. Further, it results inmore efficient repairs when used as part of the repair process.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed toward an improved inter-laminarcoating for steel laminations used in electrical equipment such aselectric motors, generators and transformers. The invention furtherincludes a process for creating, restoring, and improving the conditionof insulation of such equipment using an aqueous solution of phosphoricacid with additives including zinc and/or manganese.

The invention includes a single-step process for eliminatinginterlaminar shorts and developing coreplate. The coreplate canwithstand burnout at high oven temperatures, and the coreplate isrelatively safe, free from harsh chemicals or residue, and it does notdegrade or contaminate varnishes or resins. The coreplate is also highlydurable. Use of the process and coreplate of the invention both reduceenergy costs during manufacture of a motor, generator, or transformer,and during subsequent operation of the machine.

Other objects and features will be in part apparent and in part pointedout hereinafter.

DETAILED DESCRIPTION OF INVENTION

The following detailed description illustrates the invention by way ofexample and not by way of limitation. This description clearly enablesone skilled in the art to make and use the invention, and describesseveral embodiments, adaptations, variations, alternatives and uses ofthe invention, including what is presently believed to be the best modeof carrying out the invention. Additionally, it is to be understood thatthe invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or carried out invarious ways. Also, it will be understood that the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting.

This present invention comprises the use of an aqueous solution ofphosphoric acid, with or without a small quantity of nitric acid, andwith certain additives, to improve the formation of a coating for steellaminations used in motors, generators, transformers, etc., and toprovide the laminations with excellent properties of electricalresistance. Further, previously published research (EASA AEMT study)indicates that conventional organic coreplate deteriorates attemperatures in excess of 680° F. In accordance with the invention, thecombination of phosphoric acid, to etch the surface of the laminations,and the chemical reaction of the solution with the steel, forms aphosphate conversion coating on the surface of the laminations. Theadditives, which include zinc and/or manganese, enhances the electricalresistance of the lamination surface exposed to the solution, andreduces eddy-current losses therein. A phosphoric acid solution, withzinc in amounts ranging from approximately 0.05% to approximately 5.0%,together with manganese is amounts ranging from approximately 0.02% toapproximately 2%, is applied to the metal substrate of the laminationsas follows:

A solution of dispersion in an aqueous medium, as set forth Table 1below, was used for testing. A preferred formulation includes a 20%concentration of phosphoric acid and 1% nitric acid, together with azinc content between 0.01% and 1%, and less than 2% manganese. TABLE IParts by Weight Phosphoric acid, 200 Nitric acid 45 Zinc Phosphorate 53Manganese iron oxide, Fe₂O₃, and manganese dioxide, MnO₂,Samples of some solutions contain traces of zinc salts as impurities.

Small cores (less than 5 kW), when being rewound, have been treated byimmersion in the solution for 15 minutes. Larger cores (100-200 kW) havebeen treated by a method described hereinafter. Core losses in theelectrical equipment in which these cores are installed were reduced byover 50%. Still larger magnetic cores (up to 1500 kW thus far) have beentreated using similar methods, with similar results.

On the basis of these observations, and tests summarized in Table IIbelow, eddy-current losses in magnetic cores are considerably reducedwhich improves the electric equipment's performance by reducing lossesand thereby increasing operating efficiency and reducing operating cost,and by reducing the equipment's operating temperature and therebyincreasing the life of its windings. This latter is in accordance withthe widely accepted 10° C. rule; i.e., a 10° C. increase in windingtemperature reduces insulation life by one-half. TABLE II Test # Coreloss (watts/lb) Power factor Hot spot temp. (F.) 1 4.21 to 2.34 0.67 to0.58 128 to 83 2 3.75 to 1.96 0.70 to 0.50 109 to 74 3 11.89 to 1.82 187 to 79Reduction in core loss and hot spot temperature for before and aftertreatment.Procedure

The solution is preheated to between 160° F. (71° C.) and 210° F. (≈100°C.). The part to be treated can be immersed or sprayed with thesolution. Smaller cores are immersed in the solution while at ambienttemperature when immersed. Here, reliance is placed on heat from thesolution to heat the core. For large cores, the core is preheated tobetween 160° F. and 210° F. before immersion into the solution. Forlarger cores it is also more practical to apply the solution topically,except in instances of large volume production. One way of doing this isto use a spray bottle to apply the solution. Regardless of the method ofapplication, the surface of the core lamination should be in contactwith the solution for 15 minutes to achieve the optimal coating. Thebenefits of the solution and its application are achieved with eithermethod of application.

The chemical process is a conversion coating; that is, the surface ofthe steel reacts chemically with the phosphoric acid solution to coatthe surface of the steel laminations with a phosphate coating. Presenceof zinc and/or manganese further improves the electrical resistance ofthe coating so formed. After 15 minutes of exposure to the solution, thetreated core is rinsed in cold water to remove traces of any zinc salts.

The micro-porosity of the conversion surface has additional benefits.One is the improvement of bond strength of winding treatments to thecore after the wound core is dipped, or VPI processed. This affords abetter seal and improves moisture resistance.

Overall, the results show an average reduction in core-loss greater than50% of the before-treatment value for cores being rewound. In instanceswhere surface shorting of laminations was noticeable, the interlaminarshorts were corrected by treatment with the solution, and the reductionin core loss was even greater. Long-term benefits from applying thesolution to the cores did not appreciably lessen over the course oftests to which the equipment was subjected. Motors treated with thesolution during the research and development stage of the product havebeen running successfully in industrial applications for over one year,without failure. Comparable results are expected for new manufacture ofcores using this process.

Finally, in preparing the solution, Calcium (3.35e-8), Strontium(1.31e-7), or Barium (3.32e-7) may be substituted for the manganese,and/or Cadmium (7.24e-8) substituted for the zinc. Or, any combinationof Calcium, Strontium, Barium, and Cadmium can be substituted for themanganese or zinc.

In view of the above, it will be seen that the several objects andadvantages of the present disclosure have been achieved and otheradvantageous results have been obtained.

1. A solution for coating, or restoring the coating of an interlaminarinsulation of electrical steel laminations, comprising a mixture of: a)an aqueous solution of phosphoric acid with or without nitric acid,applied to a steel lamination; b) zinc and/or manganese in anycombination, which enhances the electrical resistance of the conversioncoating so formed; and, c) about 0.01% by weight of iron, based on theweight of a) and b), dissolved into suspension, use of the mixturereducing core losses of the laminations when used in transformers androtating electric machines including motors and generators.
 2. Thesolution process of claim 1 in which Calcium (3.35e-8), Strontium(1.31e-7), or Barium (3.32e-7) is substituted for the manganese.
 3. Thesolution of claim 2 in which Cadmium (7.24e-8) is substituted for thezinc.
 4. The solution of claim 1 further including substituting anycombination of Calcium, Strontium, Barium, and Cadmium for the manganeseor zinc.
 5. A process of applying the coating of claim 1 wherein thelaminations are preheated to approximately 160°-210° F. (71° C.-≈100°C.) before the mixture is applied.
 6. The process of claim 5 in whichthe mixture is applied by immersion of the preheated laminations intothe mixture.
 7. The process of claim 5 in which the mixture is appliedby spraying the mixture onto the preheated laminations.
 8. The processof claim 5 wherein the solution is applied by a continuous process usinga spray or a mist, or applying the solution using a roller.
 9. Theprocess of claim 5 in which the aqueous solution is applied to the steellaminations either individually, in combination, or when assembled intoone or more cores.